Other forms: transatlantically
If you fly from New York to Paris, you can describe the flight as transatlantic, since you'll be crossing the Atlantic Ocean.
Anything that crosses the Atlantic Ocean can be called transatlantic, though the word usually refers to a commercial airplane flight. Cruise ships have transatlantic crossings, and shipping companies sometimes deliver goods via transatlantic routes. The word transatlantic simply adds the Latin prefix trans, "through or across," to the word atlantic.